Pressure fluid follow-up type servomotor and control therefor



g- 1952 A. GARDE ET AL PRESSURE FLUID FOLLOW-UP TYPE SERVOMOTOR AND CONTROL THEREFOR Filed Aug. 11, 1949 PL] 0 I "nun u [lLZ/l I I'll W m 6 w M 5 M m M "H W ATTOR XEY,

Patented Aug. 12, 1952 PRESSURE FLUID FOLLOW-UP TYPE SER- VOMOTOR AND CONTROL THEREFOR Aage Garde and Ejnar Brodersen,

assignors to Allmanna Svenska Elek- Sweden,

Vasteras,

triska Aktiebolaget, Vasteras, Sweden, a Swedish corporation Application August 11, 1949, Serial No. 109,655

I In Sweden August 16, 1948 3 Claims. (01. 121-42) In water turbines, a tendency to hunting of the speed may occur, which hunting may be caused by different conditions but generally by variations in the service conditions and by changes of the delivery of water. This may for instance be the case when two or a plurality of turbines are connected to the same tube line, so that the regulation of one of the turbines will cause variations of the pressure, the magnitude of said pressure variations being dependent upon the position of the guide vane mechanism of the other turbines.

According to the present invention, such huntings are so suppressed that after a number of hunting half waves, the compensation of the regulator is changed. The invention further comprises means for the indication of the occurrence of a hunting tendency and the utilization of the said indication for the changes of the compensation.

According to one form of the invention, the motions of the guide vane mechanism of the turbines caused by the huntings are utilized for the detection and counting of the huntings, i. e. for counting of the number of the hunting half waves.

On the accompanying drawing, two different forms of the invention are shown where Fig. 1 shows an arrangement in which the motions of the guide vane mechanism are transmitted to the impulse giving member over an electromagnetic. slip coupling Whereas Fig. 2 shows an arrangement where polarized relays fed from a potentiometer actuated by the guide vane mechanism serve as impulse giving members to the counting member, which in the form shown in Fig. 1 as well as in the form shown in Fig. 2 suitably consists of a stepping relay.

The present arrangement is applicable to a control mechanism of the type shown in the patent to Lilja, No. 2,273,407.

In the illustrative embodiment shown in the drawing, the invention is incorporated in. an hydraulic governor of the type shown in the patent to Lilja, No. 2,273,407. This governor, indicated generally at I 95, is used for controlling the speed of a water-wheel turbine I03 actuating a generator I 8'! which supplies electric current to a network on which a load I09 is imposed. As usual, the turbine speed is regulated by a penstock valve I In which is adjusted, usually through intermediate hydraulic mechanism (not shown), with a rod III of a servomotor I. Herein, the latter comprises a piston I I2 mounted on the rod I I I and reciprocable in a cylinder I I3 and preferably urged in the speed-decreasing direction by a compression spring II 4.

The governor proper comprises a head I I 5 carrying rlyballs H6 and driven from the turbine prime mover I86 through a connection indicated by a broken line. The flyballs are urged inwardly by a coiled spring II8 which may be adjusted through a screw I I9 to vary the governor speed setting. The position of the fiyballs determines the axial position of a pilot piston I23 with respect to a port I2I in a sleeve I22 which is slidable axially in a valve body I22 and has a port I23 communicating through a conduit I24 with a source of pressure fluid. The lower end of the valve cylinder I23 has an outlet through a port I38 and a passage I3I. Pressure fluid flows to and from the upper end of the servo cylinder I I3 through a. passage I32 connected to the port IZI.

The mechanism usually employed to compensate for the lag of the prime mover and of the control system so as to prevent hunting includes a sleeve I22 which carries a piston I 33 reciprocable in a receiving cylinder I34 and urged by a spring I35 toward a neutral position. A trans mitting piston I33 moves with the servo piston II2 to cause oil trapped in the lower end of the piston cylinder I37 to flow to and from the-receiving cylinder I34 through a passage I38 having a leak port I39 therein adjustable by a needle I40. The valve chamber has an outlet I4I The arrangement thus far described is'typical of the compensating type of hydraulic governor controls to which the present invention is particularly applicable.

A supplementary compensating means includes an hydraulic actuator connected in the fluid compensating circuit and operable to vary the pressure therein instantaneously in response to load changes. The actuator herein shown comprises a third cylinder I43 the head of which leads to the compensating chamber through a passage I44, the connection being to the cylinder I31 in the present instance. A piston I45 in the cylinder I 43 is urged in a pressure increasing direction. by a spring I46 and the piston rod I47 is connected to an electric actuator I48 the energize.- tion of which varies with changes in the load on the generating system. In Fig. 1, the actuator comprises an armature I49 on the piston rod coacting with a solenoid coil I50 which is connected to the secondary of a transformer I 5| having its primary interposed in one of the lines leading from the generator I07 so as to be energized constantly.

The load compensating mechanism described above is also provided with means for adjusting the amount of compensation. To this end, a rheostat I53 is connected in parallel with the secondary of transformer ll or, in the case of the D. C. system, in series with the solenoid. By adjustment of this rheostat, the change in energization oi the electric actuator I48 for a given load change may be varied as desired. By opening a switch I54, the load compensator may be disabled completely. I

The rod HI of the servomotor l of the regulating apparatus is provided with a second rack 2 with which a pinion 3 engages. The latter coupled to an electromagnetic slip coupling con-' sisting of the two movable members 5 and 6, of which the member 5 is coupled with the pinion whereas the member 6 is actuated by springs I and 8 and is provided with a contact arm 9 with a contact it which in the end positions alternatingly closes the contact pairs II and I2.' .When these are closed, a current impulse traverses the coil 13 of the stepping relay M. The armature l5 of this relay which is actuated by the coil [3 is connected with a pawl It which for each impulse steps the ratchet wheel a step forward. The pawl I6 is normally out of engagement with the ratchet wheel I7, being held up by an arma ture lt actuated by a coil I9 and the current through this coil will be interrupted when the contact inthe relay 2! is opened, when the relay coil 22 of this relay receives current which will occur simultaneously with the current delivery to the coil 13. Relay 21 is by means of the condenser 23 delayed in the opening motion in order to enable a plurality of stepping motions following closely after each other. After a certain number of impulses for instance three, which number generally will be sufiicient to indicate-the existence of a hunting, the contact arm.

24 of the ratchet wheel I! will have moved so far that it will have closed the contact pair 25 thus .closing a circuit through the coil 26 in a relay I54 which will perform the change of the compensation. The pressbutton 28 serves for restoring the compensation to its original value after the cause of the hunting has disappeared or been F removed.

In Fig. 2, I also designates the servomotor of the regulating apparatus which in this case acts on the sliding contact 39 on the potentiometer 3 I.

relay 2 [,such as shown inF'ig. 1. Instead of using two polarized relays, it is, of course, also possible to use a single relay and then either a polarized relay with two parallel-connected contacts,

which are closed alternatively, or a single nonpolarized relay, if the latter is suiiiciently sensitive.

We claim as our invention:

1. A servomotor system for regulating a water turbine for a power station having compensating means for the said regulator, means for altering said compensating means on occurrence of a hunting, comprising an electric current control device actuated by the servomotor of the system, an electro-magnetic device energized over said control device in response to reciprocating motion of said servomotor, pawl and ratchet mechanism operated by said electro-magnetic device, a time delay electro-magnet controlling the engagement and disengagement of said pawl and ratchet mechanism, and a contact member operated by said ratchet to alter the said compensation.

2. Means according to claim 1, in which the said current control device comprises an electromagnetic slip coupling and a contact arm actuated thereby.

3. Means according to claim 1, in which the said current control device comprises a potentiometer and a sliding contact therefor.

AAGE GARDE. EJNAR BRODERSEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Lilja Feb. 17, 1942 

